An antenna (Antenna) is a converter, which converts a travelling wave propagated on a transmission line to an electromagnetic wave propagated in an unbounded medium (generally a free space), or performs inverse conversion. Engineering systems, such as radio communication, broadcast, television, radar, navigation, electronic countermeasure, remote sense, and radio astronomy, which transmit information by using an electromagnetic wave, all rely on an antenna for working. In addition, in the case of transferring energy by using an electromagnetic wave, non-signal energy radiation also requires an antenna. Generally, an antenna has reversibility, that is, a same antenna not only may be used as a transmitting antenna, but also may be used as a receiving antenna.
With popularity of handheld terminals, an antenna technology is more and more widely applied in handheld terminals. Due to a trend of developing small, light, and thin handheld terminals, an effective space in an antenna area becomes smaller and smaller; moreover, as there are many communication systems nowadays, for example, requirements of frequency bands such as 2G, 3G, and 4G need to be met, a target bandwidth is high, so that it is relatively difficult to design an antenna.